Bank the aircraft and watch the heading turn in real time. The gyro-accurate DG (right) always shows the true heading. The whiskey compass (top strip), free to swing with the local magnetic field, lags the turn approaching North and leads it approaching South — the classic UNOS/ONUS effect. A small red bug on the DG marks exactly where the whiskey compass currently reads, so you can watch the two instruments disagree as you turn.